1. Field of the Invention
The present invention relates to a driver circuit for a semiconductor laser diode (hereafter denoted as LD) with an external modulator, in particular, the invention relates to a driver for a distributed feedback (hereafter denoted as DFB) LD integrated with an electro-absorption (hereafter denoted as EA) modulator, which is often called as EA-DFB.
2. Related Background Art
An EA-DFB has been applied to the optical communication system. The EA-DFB integrates the DFB with the EA within one chip. The DFB may generate light by supplying a current thereto, while, the EA may modulate light depending on bias conditions applied thereto. The EA-DFB generally has a cathode electrode, hereafter denoted as ComC terminal, common to the EA device and the DFB device, while, the anode of the EA device is independent of the anode of the DFB device. Thus, the EA-DFB has a device with three electrodes. Japanese Patent Applications published as JP-2000-199879A and another applications published as JP-2003-149613A have disclosed drivers to drive the EA-DFB.